From 4636e70bb0a8b871998b6841a2e4b205cf2bc863 Mon Sep 17 00:00:00 2001 From: Ross Zwisler Date: Fri, 12 May 2017 15:46:47 -0700 Subject: dax: prevent invalidation of mapped DAX entries Patch series "mm,dax: Fix data corruption due to mmap inconsistency", v4. This series fixes data corruption that can happen for DAX mounts when page faults race with write(2) and as a result page tables get out of sync with block mappings in the filesystem and thus data seen through mmap is different from data seen through read(2). The series passes testing with t_mmap_stale test program from Ross and also other mmap related tests on DAX filesystem. This patch (of 4): dax_invalidate_mapping_entry() currently removes DAX exceptional entries only if they are clean and unlocked. This is done via: invalidate_mapping_pages() invalidate_exceptional_entry() dax_invalidate_mapping_entry() However, for page cache pages removed in invalidate_mapping_pages() there is an additional criteria which is that the page must not be mapped. This is noted in the comments above invalidate_mapping_pages() and is checked in invalidate_inode_page(). For DAX entries this means that we can can end up in a situation where a DAX exceptional entry, either a huge zero page or a regular DAX entry, could end up mapped but without an associated radix tree entry. This is inconsistent with the rest of the DAX code and with what happens in the page cache case. We aren't able to unmap the DAX exceptional entry because according to its comments invalidate_mapping_pages() isn't allowed to block, and unmap_mapping_range() takes a write lock on the mapping->i_mmap_rwsem. Since we essentially never have unmapped DAX entries to evict from the radix tree, just remove dax_invalidate_mapping_entry(). Fixes: c6dcf52c23d2 ("mm: Invalidate DAX radix tree entries only if appropriate") Link: http://lkml.kernel.org/r/20170510085419.27601-2-jack@suse.cz Signed-off-by: Ross Zwisler Signed-off-by: Jan Kara Reported-by: Jan Kara Cc: Dan Williams Cc: [4.10+] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/truncate.c | 9 +++------ 1 file changed, 3 insertions(+), 6 deletions(-) (limited to 'mm') diff --git a/mm/truncate.c b/mm/truncate.c index 83a059e8cd1d..706cff171a15 100644 --- a/mm/truncate.c +++ b/mm/truncate.c @@ -67,17 +67,14 @@ static void truncate_exceptional_entry(struct address_space *mapping, /* * Invalidate exceptional entry if easily possible. This handles exceptional - * entries for invalidate_inode_pages() so for DAX it evicts only unlocked and - * clean entries. + * entries for invalidate_inode_pages(). */ static int invalidate_exceptional_entry(struct address_space *mapping, pgoff_t index, void *entry) { - /* Handled by shmem itself */ - if (shmem_mapping(mapping)) + /* Handled by shmem itself, or for DAX we do nothing. */ + if (shmem_mapping(mapping) || dax_mapping(mapping)) return 1; - if (dax_mapping(mapping)) - return dax_invalidate_mapping_entry(mapping, index); clear_shadow_entry(mapping, index, entry); return 1; } -- cgit v1.2.3-58-ga151